The present invention relates to electrosensitive recording, and more particularly, an electrosensitive recording material that is resistant to abrasion or burnishing.
Electrosensitive recording materials generally consist of paper coated on one side by a resinous material with a metallic layer subsequently vapor deposited on top of the resin. A printhead or stylus is passed over the metallic layer which is burned off upon electrical actuation of the printhead thereby exposing the resinous material underneath. The resin often includes a pigment, ink or dye to provide a suitable contrast with the surrounding metallic surface. This is illustrated in U.S. Pat. Nos. 3,995,083 and 4,339,758.
The problems of print quality and stylus wear have resulted in the use of a variety of materials in the middle contrast layer. In U.S. Pat. Nos. 3,786,518; 3,831,179; 3,995,083; and 4,217,596 the contrast layer has included a lacquer coating or printing ink to enhance contrast. Amorphous silicon oxide has also been added to the contrast layer in U.S. Pat. No. 3,786,518 to enhance contrast of the exposed layer to the metallic coating and reduce wear on the stylus. However, the inclusion of amorphous silicon results in the buildup of debris on the stylus which periodically disrupts printing.
U.S. Pat. No. 4,339,758 demonstrated the use of crystalline silicon dioxide along with amrophous silicon dioxide. This resulted in a substantial reduction in the deposits of debris on the stylus apparently due to the scraping away of debris by the hard crystalline particles of silicon.
Many printers used in electrosensitive recording use a metallic or ground roller in contact with the electrosensitive recording surface to act as a ground in the form of a ground roller which runs across the metallic layer in order to complete the circuit with the printhead or stylus. Debris also tended to accumulate on the ground roller causing an interruption of the circuit and necessitating frequent cleaning. In Ser. No. 603,060 the problems raised by ground roll buildup were suitably addressed by the introduction of lubricants such as stearates into the contrast layer. The use of lubricants served to further reduce wear and the buildup of debris around both the stylus and the ground roller.
The disadvantages of using amorphous silicon oxides, namely excessive debris deposits and wear of the stylus were addressed in U.S. Pat. No. 4,217,596 which suggested the replacement of the silicon with a combustible organic mattecausing substance, preferably polystyrene or polyethylene in granular form. The polystyrene or polyethylene granules alone have been found to provide diminished contrast to the metallic layer. In U.S. Pat. No. 4,339,758 it was disclosed that polyethylene may be used as a film forming resin in conjunction with both crystalline and amorphous silica. However, since polyethylene does not dissolve well in organic solvents it does not bind adequately when used as a film forming resin in coatings employing organic solvents.
Many printers used in electrosensitive recording utilize a printhead that remains in constant contact with the metallic surface even during intervals between the printing of characters. This contact causes an undesirable stripping or burnishing of the metallic surface. This is especially true in "high contrast" printers where more styli are used in the printhead to enhance print quality. Printers such as the IBM model 3232, Axiom model EX801, models 1110-S and 1110-P from SCI Incorporated of Huntsville, Alabama, and the Sharp model DC2106 sold by Hycom, Inc., of Irvine, Calif., all use a dot matrix type of printhead. These printers require a smoother base stock that exhibits good anti-burnishing characteristics. The abrasion of the metallic surface while the printhead is in transit between successively printed characters not only contributes to additional debris and wear of the printhead, it produces a highly undesirable reduction in print quality. The inclusion of crystalline silicon as illustrated in U.S. Pat. No. 4,339,758 and Ser. No. 603,060 although producing superior results in many printing applications contributes to this burnishing. The silicon dioxide particles in the contrast layer produce hard jagged edges which protrude from the surface of the contrast material. These edges are subject to shearing as the printhead moves across the surface between printed characters.
Accordingly, it is the principal object of the invention to substantially reduce or eliminate burnishing of the electrosensitive paper when the printhead is in motion between the characters which it is generating.
A further object of the invention is to reduce the rate of wear of the printhead and the amount of debris generated by the unwanted abrasion of the surface.